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Zoology, lecture 15
Vertebrates: Chordate introduction
| Question | Answer |
|---|---|
| Chordata | One of 29 phyla of the animal kingdom with two main groups: protochordata and vertebrata |
| Phylogenesis | Evolutionary development |
| Ancestral chordate | A deuterostomic invertebrate with a dorsal notochord around which segmented muscles developed. The first two chordate classes developed from it |
| Protochordata | Lower chordate classes of invertebrate organisms: Urochordates, Cephalochordates |
| Urochordata | בנז ינרתימ a class with around 2000 species (ex. tunicata) In their tail, during their larval stage they have a notochord that disappears later in life. |
| Cephalochordata | שאר ינרתימ about 25 species in which the notochord reaches the front part of the body (head). Ex. Amphioxus ןולמזיא They have a head but no skull (acraniata) |
| Amphioxus | ןולמזיא Representative of the class cephalochordates that have a notochord that reaches their head. |
| Vertebrata | Group of chordates |
| Acraniata | Lower chordates that have no skull (urochordata, cephalochordata) |
| Craniata | Higher chordates with a skull (vertebrata) starting with cyclostoma |
| Cyclostoma | Round mouthed craniata (first with a skull) the nerve chord at the front of the body developed into brains (3) No jaws (agnathostoma) |
| Agnathostoma | Jawless chordates (lower chordates all the way through the cyclostoma) |
| Gnathostoma | Chordates with jaws, starting with the class of fish continuing through the rest of the vertebrates. |
| Amphibia | First chordates to go up on land. Did this through a lot of developments namely the development of four limbs (tetrapoda) called amphibia because embryonic development is still constrained to an aqueous environment. |
| Tetrapoda | Development of four limbs that first appeared in the amphibians that allowed for their move to dry land. |
| Reptillia | Class of vertebrates that solved the amphibia dry land problem of embryonic development with the help of amniote development (all sequential vertebrates are amniotes) |
| Amniota | All vertebrates (starting with reptiles) that are capable of reproducing on dry land. |
| First group of pure land animals | Reptiles cause they solved the embryonic development problem by developing special structures for embryonic development. |
| Two directions of development from the reptiles | Aves (birds) and Mammals |
| Birds | Developed wings allowing them to fly and conquer the sky. |
| Mammals | Developed glands that allowed them to feed their young. Their brains also developed more. |
| Protochordates | Early chordates including the two groups urochordata and cephalochordata |
| Tunicata | Another name for urochordata. They are enterocoelic. |
| Urochordata embryonic development | They have a notochord along their entire tail. When they settle the notochord disappears and it is non-existant in the adult. |
| Enterocoelic | The coelom develops from outpouchings in the gastroderm. |
| Cephalochordata | (Acraniata) Believed to have led to the vertebrates. Ex. Branchiostoma aka amphioxus |
| Branchiostoma | Another name for amphioxus--a species of cephalochordata, one of the protochordate groups. They have a notochord near their head. |
| Amphioxus | ןולמזיא A species of cephalochordata (also called branchiostoma). They breath through their numerous gills. |
| ןולמזיא | Amphioxus, a species of cephalochordata |
| What are the dominant characteristics of the chordata phylum? | Skeletal axis called chorda (notochord), hollow dorsal nerve cord, deuterostomia, post anal tail and pharyngeal gill slits (found in ALL during at least some life stage) |
| All chordates have a notochord | All organisms with a notochord are chordates |
| What are the less dominant characteristics of the chordate phylum? | If there is a heart its ventral, arterial branches to the gills, bilateral symmetry, muscular segmentation around the skeletal axis, developed coelom. |
| If a chordate has a heart, where is it? | Ventral (amphioxus don't have a heart, they have a circulatory system with a main ventral tube from which the heart develops) |
| Pharyngeal slits in amphioxus | They are nonfunctional--they don't function in respiration in all chordates. But in amphioxus there are already arterial circulatory arches that branch to them. |
| Which chordate groups are bilaterally symmetrical? | All of them. |
| Amphioxus characteristics | Notochord, hollow dorsal nerve cord, deuterostomic, post-anal tail, pharyngeal gill slits, segmented muscles, simple digestive tract, hepatic diverticulum, developed coelom, bilateral symmetry, acrania, no brain. |
| Hepatic diverticulum | Or liver bud is a precursor to the liver found in amphioxus (cephalochordata) |
| Where does the nerve chord develop? | ALWAYS above the notochord. |
| Where are the gill slits in amphioxus? | At the front of the digestive system--the pharynx. They are not used for respiration. |
| How do amphioxus breath? | Diffusion through the body wall (they are very thin so the oxygen can reach their internal organs) |
| Hepatic cecum in amphioxus | Blind protrusion from the digestive system of amphioxus. Some believe that it participates in digestion. Some say like a live, some say like a pancreas. |
| Why is there a difference of opinion as the the purpose of the hepatic cecum in amphioxus? | Cause both the liver and pancreas in later chordates grow out of the digestive system. |
| What is the function of the gill slits in the amphioxus? | They are part of the digestive system and they catch food particles and pass them through the digestive system. |
| Amphioxus coelom | They have a coelom along their entire body cavity but it is not segmented (they have no heart) it is clear and developed from the pharynx along the entire body cavity. |
| What is the amphioxus nervous system? | It is a simple hollow nerve chord with no brains and no skull. |
| Other amphioxus characteristics | Single epithelial layer, closed circulatory system, no heart, arches to the gills, blood contains no pigment to carry oxygen-respiration is through diffusion, hints of hormonal glands. |
| Hints of hormonal glands in amphioxus | Endostyle, Hatschek's pit, Kolliker pit |
| Endostyle | Evolves into the thyroid. On the underside of the pharynx there is a canal made of ciliated cells that secrete mucous that sticks to the food particles that the cilia then move along the digestive system. |
| Hatscheck's pit | An upwards outpouching from the roof of the mouth towards the area of the future brain that could be the start of the hypophysis. |
| Kolliker pit | A pit in the area of the future brain in amphioxus that is similar to the epiphysis (pineal gland) |
| Why do amphioxus have just one layer of skin? | They breath through diffusion so they need thin skin. Fast and efficient intake of oxygen through the body wall. |
| What is the structure of the circulatory system in amphioxus? | As opposed to invertebrates the system is closed. The blood flows in a particular direction from the ventral tube through the gill arches (even though there is no absorption of oxygen from the gills) |
| How many dorsal blood arteries are there in amphioxus | At the front there are two and they join into one at the back of the body. |
| Why is amphioxus blood transparent? | It doesn't carry oxygen (which travels on pigment) |
| What is the purpose of the amphioxus circulatory system? | To distribute nutrients to all the parts of the body and remove waste. |
| How does blood pump through the amphioxus body? | There is no heart (it's peristaltic contractions that pump the blood) through the ventral to the dorsal and all the way through. |
| Why do we think that the endostyle is a precursor to the thyroid gland? | Cause if you inject an amphioxus with iodine it concentrates at the endostyle, a human at the thyroid gland. |
| What is the indication of evolutionary development of the endostyle into the thyroid? | The endostyle is an exocrine gland but the thyroid is endocrine but there are leech larvae that show the closing of the same area making it go from exocrine to endocrine. |
| Hypophysis | Part of the vertebrate brain found above the oral cavity that controls a lot of other hormonal glands. It develops from two outpouchings in the body (one from the top of the mouth, one from the bottom of the brain. |
| What indicates that Hatchek's pit is a precursor to the hypophysis? | Chinese researchers saw that it reacts to antibodies to hyphysal hormones. |
| Adenohypophysa | The parallel part of the hypophysis to hatchek's pit. |
| Epiphysa | (Pineal gland) A protrusion from the middle brain upwards in vertebrates, Kolliker's pit in amphioxus is a hint to it. |
| Vertebrate characteristics | Dorsal skeletal axis made of bones to which appendage tendons are connected, two pairs of fins that became limbs. Craniata, skull, gill skeletal structure whose cartilage is produced by the neural crest, 5 brains, 10-12 pairs of nerves. |
| How many body segments are there in vertebrates? | 3--head, chest and tail. In land animals there is a neck after the head segment. |
| What is the vertebrate skin structure? | Skin made of multilayer epidermis and dermis. |
| What is the function of pharyngeal gill slits? | In cyclostoma and fish they are lined with muscles that pump water over them for respiration. |
| What is the vertebrate heart structure? | They all have a ventral heart with 2-4 chambers from which the arterial arches come out towards the pharyngeal slits and connect with the main dorsal artery |
| What is the vertebrate digestive system? | A complex digestive system with differentiation to different parts and numerous glands in addition to the two main glands (liver and pancreas) |
| What is the difference between blood vessels in amphioxus and in cyclostoma or fish? | They all pass over the pharyngeal slits but in amphioxus they function in digestion while in cyclostoma and fish they function in respiration and oxygen transfer. |
| Pericard | Part of the segmented and developed coelom that is around the heart in most vertebrates. |
| Peritoneum | Part of the segmented and developed coelom that is around the stomach in most vertebrates. |
| Excretory system in vertebrates | Highly developed organs mesonephros and metanephros kidneys. |
| Reproduction in vertebrates | Dieocious, reproductive organs have tubes that lead out of the body. |
| Who were the first vertebrates? | Cyclostoma (example lamprey דמצ) |
| What is the spinal structure of cyclostoma | They have a spinal cord but its not divided into vertebrae. They do have a solid gill structure. |
| Petromyzon | דמצ a species of cyclostoma |
| Ammocoetes | Larvae of דמצ a type of cyclostoma look a lot like amphioxus. |
| Sea lamprey life cycle | They live 3-7 years in the ground as ammocoetes (larvae) they metamorphosize into their parasitic stage on fish. They reproduce in streams and live 2 years as adult parasites. |
| What is the connection between amphioxus and ammocoetes? | They are very similar but the ammocoetes already has more advanced structures like the thyroid that is already becomeing endocrine (it's exocrine in amphioxus) |
| What always must develop next to a functional respiratory system? | A system of circulatory vessels towards the heart. |
| What is new to the ammocoete circulatory system? | They have a more branched system so they need a pump so you see the development of a heart to pump the blood over the gill slits that are used for respiration. |
| What are the stages of spinal axis development in ammocoete? | They start with a notochord over which cartilage develops making it a cartilaginous structure but STILL NOT DIVIDED INTO VERTEBRAE. |
| How many brains do cyclostoma have? | 3 |
| What are the similarities and differences between amphioxus and vertebrate skin? | In amphioxus it's just one epithelial layer (to allow for diffusion/gas exchange for respiration) while in vertebrates its multi layer. But they both have an external covering of epithelial cells. |
| What are the similarities and differences between amphioxus and vertebrate blood? | In amphioxus the blood has no oxygen carrying pigment, there are no blood cells and there is no heart, but both have a one-way closed system. |
| What are the similarities and differences between amphioxus and vertebrate skeletal systems? | Amphioxus have just a spinal axis notochord and no skull. Both have a notochord at some point during their life cycle. |
| What are the similarities and differences between amphioxus and vertebrate digestive systems? | Amphioxus are filter feeders and digestion takes place within the cells. But both are deuterstomic with a pharynx |
| What are the similarities and differences between amphioxus and vertebrate horomonal glands? | Amphioxus have no functional hormonal glands. They both have Hatschek's pit, Kolliker's pit and an endostyle. |
| What are the similarities and differences between amphioxus and vertebrate nervous and sensory systems? | Amphioxus have no brains so there is no central nervous system. But both have a dorsal nerve cord, concentrations of sensory cells and segmented spinal cord nerves |
| What are the similarities and differences between amphioxus and vertebrate excretory system? | Amphioxus have flame cells, no kidneys and secretion into the atrium cavity. Both have nephridia that are functionally similar to protonephrous. |
| What are the similarities and differences between amphioxus and vertebrate body cavity? | The amphioxus coelom is enterocoelic while in vertebrates there is a schizocoel that develops in the rear segments (like in lampreys) |
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YaelNoa
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